Protease-containing liquid aqueous detergents are well-known, especially in the context of laundry washing. A commonly encountered problem in such protease-containing liquid aqueous detergents is the degradation phenomenon by the proteolytic enzyme of second enzymes in the composition, such as amylase, lipase, and cellulase, or on the protease itself. As a result, the stability of the second enzyme or the protease itself in the detergent composition is affected and the detergent composition consequently performs less well.
In response to this problem, it has been proposed to use various protease inhibitors or stabilizers. For instance, various references have proposed the use of the following compounds to aid in the stabilization of enzymes: benzamidine hydrochloride, lower aliphatic alcohols or carboxylic acids, mixtures of a polyol and a boron compound, aromatic borate esters, and calcium, particularly calcium formate. Recently, it was discovered that certain peptide aldehydes and trifluromethyl ketones act to stabilize protease enzyme.
Although these compounds have been used to varying success in liquid detergents, they are not free of problems. For example certain peptide aldehydes can be rather expensive and create complexities for the formulators, especially for liquid detergents. Other inhibitors such as calcium and boric acids are less expensive but do not stabilize enzymes as well as peptide aldehydes. It is thus an object of the present invention to provide a protease inhibitor which is economical, effective and suitable for use in a liquid detergent composition.